Identifying Victorian Gun Emplacements

Slide

The term 'slide' is interchangeable with 'platform'. In some documents both terms are used.

Pivot

The real or imaginary point about which a gun is traversed is referred to as the Pivot.
By the 1880s they were classified as :-

A pivot The imaginary pivot is in front of the platform, in the embrasure.

B pivot Similar to A.

C pivot The pivot is central and the racer a circle.

D pivot The pivot is nearer to the rear of the slide than to the front.

E pivot Similar to D.

F pivot The pivot is behind both front and rear racers.

The A & B pivot usually give a field of fire of 70 degrees. The
C pivot gives 360 degrees whilst the D gives 180 or 360 degrees. The E
& F pivots give 180 degrees. A pivots are suitable for embrasures;
D pivots for barbette emplacements with less than 140 degrees of
lateral training and C pivots for barbettes with a larger amount.
Casemate slides are used only with A pivot racers.

Dwarf slides are suited to all pivots. D pivots were not much used
except for the colonial carriage. E & F pivots were specially
designed for the tops of Martello towers and are rarely found
elsewhere. In C and D pivots the actual pivot is usually an old gun, a
24 or 32 pr. S.B. set in concrete. An alternative is a cast iron pivot
block.

The term Platform or Traversing platform was the official
nomenclature for what was later referred to as a slide in official
handbooks and documents. Platforms for medium and heavy guns were often
described according to the type of pivot they required e.g. Slide,
7-Feet Parapet C Mark II.

Pivot Block

The block about which the slide rotates and
to which the slide is connected is known as the Pivot Block. All medium
guns on C, D, E or F pivot racers require actual pivots. This consists
of a cast iron block into which a steel plug three inches in diameter
fits passing through a plate on the underside of the slide. The height
of the pivot block depends on the type of slide used. It could be 12.25
inches or for the high block 18.375 inches. For some heavy RML
emplacements old smooth bore guns were used as the pivot. These were
one of three types, the 9pr. of 4.2 inches diameter, the 18pr. of
5.3-inches diameter and the 24pr. of 5.82 inches. These were approved
for all calibres and you cannot therefore identify the type of gun and
platform used by the nature of the pivot where it is an old smooth bore
gun. The pivot performs some useful function in taking up part of the
force of recoil. Where there is no pivot this has to be taken entirely
by the racers. We found from the experience of firing a 32pr. S.B.B.L.
gun in the caponier at Fort Nelson, where no pivot had been fitted,
that the force of recoil can impose a strain on the trucks, which were
cast-iron. In this case the relatively small force of recoil obtained
from a small blank charge caused one of flanges of one of the front
trucks of the slide to shear off. A pivot would have absorbed most of
this force.

Racer Track. (Racers)

The curved track set into the floor
of a gun emplacement which enabled guns to be traversed more quickly is
the racer track. Racers for guns up to 10-inch are of wrought iron 27/8
inches wide. Racers of 10 inch R.M.L.s and above are of steel. 12-inch,
35 ton and 12.5 inch, 38 ton guns employ heavy racers 4 inches wide
without flanges. 20 pr & 40 pr R.B.L.s required gun metal
racers, ribbed and slightly coned towards the pivot. Racers are fixed
on iron chairs or set in granite blocks.The configuration varies
according the the platform and method of mounting and the position
depends upon the pivot.

Slide designations

Three heights of slide (platform) were
employed for medium and heavy guns, the Casemate, Dwarf and Blocked-up.
Curiously the casemate platform is lower than the dwarf. For heavy guns
only casemate and dwarf platforms were employed with, in addition, many
special platforms to suit particular needs, such as high angle, long
range, turntable, small port, short recoil, sunken way etc. The
casemate platform was only used inside a casemate where height was at a
premium. In open emplacements dwarf and blocked up platforms were used.
The blocked-up platform is basically a casemate platform with
heightened rear and front blocks, possibly with a change of trucks to
suit. Most can be fitted with pivot plates to suit B, C or D pivots.

Space for the 16ft. slide.

The space to be kept clear for a 16ft slide are as follows:

A Pivot emplacement

From the front racer to the front - 1ft. 6-in

From the pivot to the rear - 20ft.

C pivot emplacement

From the pivot to the front - 7ft. 6-in

From the pivot to the rear - 9ft. 6-in

D pivot emplacements

From the pivot to the front - 10ft.

Six-feet Parapet Slide. (6ft. Parapet Platform)

This was
specially designed for use in coast batteries. It was of wrought iron
and was mounted on live rollers to fire over a 6ft. parapet. It was
13ft. 2ins long and used the same racers as the 16ft. slide. The 64 pr
of 64cwt. and the 80pr converted guns were to be mounted in this way.
Later the 7-inch 6½ ton R.M.L. in the land service was given a
slide of this nature. It was referred to as a blocked-up slide and
consisted of firstly blocking up the slide to enable the parapet to be
raised to a greater height above the racers. The mounting gave security
to the detachment against all projectiles except those fired at high
angles. The elevating gear was altered so that the crew could load the
gun under cover at depression. It was an adapted dwarf platform raised
by an additional 1 foot 10¾ inches enabling the gun to be fired
over a parapet 5ft. 10½ high above the top of the racer and
therefore 6ft. above the racer blocks. This improvement could be
applied to all emplacements whatever the pivot letter type.

With a C pivot the radius of the emplacement should be 9ft. at top.
A similar mounting was experimented with the 7-inch 7 ton gun. The
pivot block is 18.375 inches high instead of 12¼ inches and it
takes a pivot plug of four inches diameter instead of three inches,
which the low mounting requires.

Shortened 13-Foot Slide.
This was a traversing platform
for use with the converted 64 pr and 80pr guns and with the 7-inch
R.B.L. It is the old 16ft. slide with three feet cut off and provided
with a hydraulic buffer and the wooden slide replaced by a wrought iron
one. New casemates for these guns had a sill height of 4ft. 3-ins or
3ft. 6-ins whilst the earlier sills were 2ft. 3-ins.

Shortened 11-Foot Slide.
This was a traversing platform
intended to take the 7-inch R.B.L. for use in Great Britain only.
Designed for mounting in the flanks of forts where it could be easily
blinded, it fired over a sill 3ft. 6ins high. It was possible to mount
a 64 pr. on it, although not recommended. A blocked up 11 ft. slide was
produced for 6ft. parapets.

Identifying platforms by their emplacements

The type of
armament employed depended on the location of the fort or battery. Land
front defences did not employ anything larger than the 64pr. RML as the
main armament on front faces (with 7-inch R.B.L., on flanks)
whilstCoast Defence forts and batteries employed the 7-inch of 7-ton
RML upwards. Recognising the various type of mounting for medium guns
on land front forts is a matter of experience. Often it helps to look
at the armament return for the fort concerned and cross reference this
with the plan of the fort, where available, to identify each gun
emplacement. A pivots rarely have a real pivot block. The exception
appears to be those for the adapted naval broadside mount, examples of
which can be found at Whitesand Bay Practice Battery and Pendennis
Castle. Because the actual pivot point of an A pivot cannot be
accurately determined it can be easier to find out the type of platform
mounted on a land front A pivot by measuring the distance between the
front and rear racers and the height of the sill of the embrasure. For
example the No.13 medium platform had a front racer radius of 5ft and a
rear racer radius of 14ft. This gives a distance of 9ft between racers.
A height of 3ft. 6in for the parapet would suggest that the emplacement
was for a Platform, Wood Traversing, Medium No.13 for 7-inch RBL or
64pr. RML

Racers for Medium Slides

Racers for Heavy RML Guns

Casemates

Platforms employed in casemates can be treated
in the same way. It is safe to assume that these will be casemate
platforms on A pivots. No actual pivots will be found in casemates.
Lewis gave the reason for this as being the necessity for putting the
position of the pivot far forward, in order that the size of the shield
opening may be at a minimum, and would make it impossible to secure an
actual pivot against the chance of injury from a shot striking the
shield; and as, if displaced, it would prevent the gun being traversed,
it was therefore thought better to omit it altogether, and to take up
the recoil entirely by the racers. This did mean that considerable
inconvenience was caused in connection with position finding because of
the lack of any means of accurately centering the slide when being
traversed, it is apt to get slightly askew, and not always to lie on
the bearing indicated on the training arc. On land front forts Haxo
casemates were armed with the 7-inch RBL or the 64pr. RML. on an A
pivot platform. Measuring the height of the sill and the racer radii
will identify the platform.

In open embrasures on land front forts dwarf platforms were often
used. For positions that were liable to enfilade such as the front
faces of forts six foot parapet slides were often used. These took the
form of a circular concrete plinth or drum with a circular racer and a
central pivot block

Coast defence open barbettes.

Emplacements to take dwarf slides.

Muzzle loading guns on dwarf slides for C or D pivots are mounted in
a pit over the edge of which they fire. If on an A pivot they are
mounted in an emplacement similar in plan to a casemate and fire
through a shallow embrasure, the sole of which is 4ft. 3-inches above
the racer.

The dimensions for C and D pivot emplacements, which are called
barbette emplacements, depend on the method of loading the gun. Older
forms of barbette emplacements for heavy guns were copied from those
for S.B. guns, the height of the parapet above the racer being the same
and being still retained. The maximum radius possible for the
emplacement was determined by the necessity of the the muzzle of the
gun to project at least a foot over the parapet when run out to fire,
the minimum by the the necessity of getting easily at the muzzle to
load when the gun was run back. As the guns increased in size the
height of the axis of the bore above the floor of the emplacement
increased until it became too great for convenient working and so the
Fixed Loading Stage was introduced.

Emplacement with fixed loading Stage.

To meet the increase
in size of the gun the emplacement was increased in size and a a fixed
step or loading stage, was carried around the front of it. This step is
7-inches high for 10-inch and 11-inch RML guns. The 7-inch and 9-inch
guns required none. This enabled the loading numbers to stand high
enough to enter the the charge and ram home and allowed the projectile
to be raised vertically to the muzzle without striking the parapet.
Many emplacements like this for guns under 35-tons were used.

Platforms used for coast defence in open barbette positions were
often those designated as C for sunken way. These tended to be adapted
from ordinary dwarf platforms. They were fitted to an emplacement that
afforded greater protection to the crew, who were unnecessarily exposed
to fire whilst loading in the old type loading-stage pits.

Designated as 'Emplacements with Sunken Loading Way and Movable
Loading Stage' they had a trench, or loading way, cut round the front
of the emplacement where the old step had been, to a depth of 7ft.
below the crest, thereby protecting the crew standing in it. In this
trench a wooden stage was arranged to run on rails so that the men
standing on it could reach the muzzle of the gun to enter the charge.
the ground behind the gun was lowered so that it was standing on a drum
or irregular shape approached in rear by a ramp or two or three steps.

Later form of barbette emplacement

A further refinement
was made to these emplacements by fitting the slide to a circular drum
carrying the racers. the traversing gear was altered to work from the
7ft. level below the crest and a convenient crane for raising the
projectiles was supplied instead of the old muzzle derrick fixed on the
gun. The stage was fixed to the slide instead of running on rails.
These emplacements can be identified by their diameter, height, the
width of the emplacement, the height of the parapet and other features
such as the steps cast in the drum for the crew to mount. In all
emplacements of this type for 10-inch and 11-inch RML guns the drums
are circular with a radius of 8ft. 3-inches, the top, to a depth of
6-inches being formed to a radius of 8ft. 1 inch to give a clearance to
part of the traversing gear. The drums for the 9-inch guns were made to
a radius of 6ft. 3-inches in front and 8ft. in rear to provide
additional support to the racer.

Training arcs for both C and D pivots.

12.5-inch gun - 6ft. 9-ins

12 -inch 11-inch 10-inch - 7ft. 9-ins

9-inch - 5ft. 10-ins

Coast defence casemates

The sea defence casemated
batteries were armed with the 7-inch of 7-tons upwards. The large
casemated works such as Gilkicker, Hurst, Bovisand, Garrison Point etc.
often had a mixture of 9-inch and 10-inch in the casemates with larger
11-inch and 12 or 12.5-inch on the upper roof battery. Only guns of
10-inch and upwards were fitted with mantlets and the presence of
mantlet bars is therefore a clue that the gun occupying the position
was at least a 10-inch R.M.L.

Overhead Loops.

These rings, two or three fitted in the
overhead vaulting of heavy gun casemates used for mounting the gun on
its carriage, can be an aid to identifying the gun employed. The loops
are placed in the centre-line of the casemate, facing to the side,
their positions varying according to the nature and weight of the gun
employed. The distances from the pivot of the gun are given by Lewis as
follows;-

gun -----front ------middle ------rear

12-ton-- 6‘ 6• ---------------------17‘

18-ton --9‘ 0• ---------------------19‘ 6•

25-ton --6‘ 6• -------13‘ 6• -----19‘

38-ton --6‘ 6• -------16‘ 6• -----22‘

Lewis does add that the positions of loops for other guns would
probably be different, depending on the mode of mounting adopted, and
the positions of the centres of gravity of the guns.

Caponiers.

I have yet to find a caponier that has racers
fitted for anything other than a 32pr. S.B.B.L. gun. I can safely state
that this was the standard armament of caponiers for guns on traversing
platforms. The only alternative to this was the use of carronades and
these were not mounted on traversing platforms therefore no racers will
be found. This does not mean that the absence of racers is evidence for
carronades being employed. The only real proof is the armament return
for the fort concerned.

One example of a emplacement that adds confusion is Fort Staddon, at
Plymouth. Here the armament return states quite plainly that the
caponiers were fitted with 32pr. S.B.B.L. guns, but measurements made
of the extant racers showed the following :-

This gives a difference between the racers of 39ins. The 32pr.
should have racers with a front radius of 1ft. 6in and rear of 6ft.
10in giving a difference of 64 in. The armament return shows 32prs.
mounted so the platform must have been a special adaptation with the
rear trucks moved further in. This is the only example of such a
modification found so far and may be due to the fact that Plymouth
received the first allocation of 32prs. for flank defence.

Sources

A Handbook of Military Terms used in Connection with Fortifications of the Victorian Period by David Moore. Published by The Palmerston Forts Society. ISBN 0 9523634 2 9Permanent Fortification for English Engineers - Lewis